Process of coating fibers with gas agitation



value.

, twine forming clumps of fibers.

. for coating pulp fibers with rubber.

.when the rubber latex and coagulant were added to the pulp in the beater, the result indicated that Patented Apr. 26, 1954 UNITED STATES PATENT OFFICE PROCESS OF COATING FIBERS WITH GAS AGITATION John Y. L. Kao, Chicago, Ill., assignor to F. D. Farnam 00., Chicago, 111., a corporation of Illinois No Drawing. Application September 25, 1948, Serial No. 51,294

'1 The present invention relates to a process for coating animal, mineral or vegetable fibers, and

particularly to a process for coating such fibers while in the pulp state with any material which can be emulsified.

There are in commercial use today many methods of coating fibrous material with a coating either before or after the fibrous material has been formed into sheets. Of these processes, the

present invention is concerned only with those wherein the pulp is treated prior to being formed into sheets.

The conventional means and methods for treating pulp with latices or emulsions of resinous maconcentration of the pulp to as high as 5% or 6% because this prior process at best is slow and if,

a lower concentration were used it would raise the cost of the process to an uneconomically high However, with the pulp at this high concentration the fibers tend to entangle and interthe pulp slurry is high and as the pulp slurry is passed through the beater, there is little or no dispersion of the fibers in the water or pulp liquoronly the slow movement of a stream or mass of pulp fibers except when the pulp passes 5 through the beater blades at which time its movement is greatly accelerated.

This prior art process was primarily developed However,

the rubber coated the outside of. the clumps of fibers with only a small percentage of rubber. It is obvious that with the rubber coating primarily the outer surfaces of the clumps that all of the fibers in the pulp will not have a uniform coating of rubber.

Because the pulp slurry has a high viscosity neither the latex nor the coagulant will be properly dispersed and local high concentrations of latex or coagulant will occur causing local and spotty coagulation of the latex to form clumps of rubber and rubber threads. This. is particularly true of latices which are not properly or completely stabilized. These rubber formations and clumps of pulp plug the screen during the The viscosity of.

5 Claims. (01. 92--21) 2 paper making and will also damage the pump and flow conduits.

Another reason for the presence of clumps of rubber in the pulp slurry is in the use of the beater to circulate the pulp during the prior art process. As the pulp is circulated the clumps of pulp coated with rubber come into direct contact with the rapidly rotating blades. Since the rubber is not firmly attached to the pulp fibers, it may beand frequently is-stripped off and small particles of coagulated rubber will be free in the pulp slurry.

It is obvious that the prior art process produces a pulp that is very diflicult to work on the paper or sheet forming machine. The finished product lacks uniformity due to the'loss of rubber in the formation of clumps of rubber and due to the uneven distribution of the rubber on the pulp fibers. This lack of uniformity is demonstrated by corresponding deficiencies in the physical characteristics of the finished sheet product.

As a result of these difficulties it is not commercially feasible, using' the prior art processes, to manufacture a finished product having a uniformly deposited material content of greater than about 20% of the weight of the product.

The principal object of the present invention is to provide a novel process of coating fibers'in the pulp stage with an emulsifiable material which overcomes the foregoing dimculties of the prior art processes. 7

Another object is to provide a novel process for treating fibers with an emulsifiable substance wherein the finished Product may contain up to 55% or more of the deposited coated substance by weight. I

Another object is to provide a novel process for treating fibers in the pulp stage with an emulsifiable substance wherein the fibers are so agitated and dispersed that each individual fiber is uniformly and'evenly coated with the substance.

Another object is to provide a novel process a for coating fibers in the pulp stage with an emul- 'sifiable substance wherein the treated pulp is substantially free from rubber or resinous lumps,

clumps of fibers or uncoated fibers.

substance can be emulsified and can be added to the pulp in the form of an emulsion.

Another object is to provide a novel process of coating fibers in the pulp stage wherein the pulp is agitated in such'a manner as to reduce the :in commercial use.

3 coating time to under that required by the prior art processes.

Another object is to provide a novel process of coating fibers in the pulp stage so that the finished product has highly uniform physical properties.

Another object is to provide a novel processof coating fibers in the pulp stage wherein the pulp concentration in the slurry is substantially lower than that used in the prior .art. processes.

Another object is to provide a novel'process of coating fibers in the pulp stage wherein the means for agitating and dispersingztheipulpfibers includes no mechanical 'devices such-as beaiters or pumps or agitators and wherein the agitation and dispersion are more completerthanlin the prior art processes.

Other objects and advantages will become apparent from the following description. There are no drawings.

The present invention contemplates processing animal, mineral and vegetable fibersand nondistinction among these..ifibers will be made (in this specification. Examples of ifibers :that :may .be processed are wool "and "leatherfibersljianimal) asbestos (mineral), and woodiand other cellulosic fibers (vegetable). In the'specific examples set the .preparationio'f.thepulp, it may be prepared according to any one of the various processes now At the end of the beater operation the 'pulptshould be diluted to'a concent-ration of 2%xor:less'and;preferably. 1% or under. This low' concentrationiis preferredbe- .cause at this concentration :there: is .littleonno tendency to form :clots .or clumps "of fibers as is .the :caseLwith pulp :slurry in its-normal concentrationprior .to dilution. Furthermore, the "vis-'- cosity ofthepulp slurry approaches that of water which: makes its agitation easier thus'increasing the dispersion of the 'fibers to increase the surface area of the fibers available for coating.

The pulp slurry-is transferred to .anagitation tank which preferably is a cylindrical vessel wherein the side-walls :curve into :the bottom, which may beconcave, so as to'remove anysharp corners or crevices whichcould create dead spots Y .or.localeddycurrents which would upset'or disturb the regular and even-though very turbulentagitation of the pulp slurry. Agitation is not-carried out by any-mechanical device but-by means of air or a gas which is'substantially water insoluble and non-reactive :with :water, pulp"or' added substances and which is introduced through strategically located jets or -outlets in 'the bottom of the tank. The locatiomof the 'jets or .outletsforms no part of .the'present-irrvenrapid so as tofaciIitate the dispersion of :the fibersand the emulsion .or latex. 'As the air bubbles to the surface of theliquid in-the-tank it expandsalso to aid'in the dispersionof .the

. pulp fibers.

The gas which isused-is preferably air, nitrogen, or a ,similargas which is substantially .in-

solublev in water and has no chemical effect upon thepulp, emulsion .or latex. .However, theremay be. occasions when .a gasmay .be chosenfor its chemical activity-such as chlorine-so as to ob tain a particular result. It is preferred that air be used because it may be compressed and filtered in the mill without the necessity of allocating storage space for tanks as would be the case weremitrogen to be used. It isaessential that the gas be .freeifrem dust, fidirt andiotherimpurities. The gas is admitted to the tank at such a rate ins to obtain a complete and substantially inawh'ichisarlded to the agitated pulp at a controlled rate.

.iAfte'r" thefpulp..-has been transferred to the agitation tankyait is agitated as described and the agitationis continued until the end of the process. Next the coagulant is added to the ebullientslurry and the agitation is continued for five to ten minutes or such a time as is necessary forthe coagulant to be thoroughly mixed with or dispersed in the pulp ifand for it to be adsorbed -=onto-the surfaces inf the=pulpfibers before the emulsion isadded. Thecoagulantiisin'the form of "fpoly-valent cations,- suchas the water (soluble salts ofoalcium, aluminum and thorium. It is not practical to use a monovalen-t'cation since rtoo large a volume of coagulant is. necessary to ,prov-ide the necessaryelectrical charge. The co- ,agulantis added in such quantities and concen- :trations-as required for the different emulsions .and latices.

While all the coagulant can-be added atrone time, it is preferable that the coagulant .be :addedin two portions, the first :portioncontain- .ing less than the-calculated totalamountofco- .agulant required. and .thesecondportion con- ..taining. the remainder of .the: coagulantsubstantially diluted. .It v.is preferred that the first portion of coagulant .be .between..50% and-90% ..of .the amountrequired .depending upon ..the

.nature and character .of the. pulp fibers and the :emulsion; less than does .notTs'eem to .be

-satisfactory.

It is known that mostof the pulp fibers are a negatively charged or .can easily be rendered .negativelycharged. Fibers of this charge .have a great-tendency .to adsorb the polyva'lent cations .and thus to form on their surfaces a layer of ;positive charges, which .will attract the negatively charged resinous or rubber particles. 'Due to the character of the 'coagulantits water "'solubilitv.-it will be adsorbed evenly by the 'jfifibers. "The power of the coagulant to uns'tabilize y'the emulsified material is dependent upon the "total power of the electrical charge. Therefore, for the equivalent concentration of coagulant,

"thorium. a tetravalent cation, will have more coagulating power than aluminum, a trivalent "cation, and aluminum will be more 'powerful'than calcium, a divalent'rcation. V *must be used soas not to add. an excess of'coagu- Consequently, care 'thepulp before the addition of the emulsion or of the emulsion .or latex.

than all of the required coagulant be added to latex.

' The next step in Ithe'process 'is' the addition. It is added at such a rate that it will substantially immediately dis- Derse into a pulp slurry. To accomplish this most effectively the emulsion or latex should be J fed directly. into the center of the agitation, either -dropwise orin .a small stream. .TheLresinousor rubberparticles will be attracted to .the"fibers above.

- by their positive charge and will be evenly deposited thereon due to the evenness of the distribution of the charge. There will be no clumps of fibers because the gas agitation keeps the'fibers well dispersed and moving constantly with both turbulent and mass movement. No lumps of resin or rubber will be formed because there is no excess of coagulant and because the particles are attracted to the fibers before they can be attracted to each other.

The emulsion or latex may or may not require the use of stabilizers, such as ionizable or nonionizable soaps, and protective colloids, such as casein, glue and haemoglobin. The emulsion or latex preferably is diluted to a concentration of between 5% to by Weight of solids, although more dilute concentrations appear to be satisfactory.

As the addition of the emulsion continues the pulp liquor may become milky, and the viscosity of the pulp will increase due to the addition of the solids. It may be necessary to increase the rate of air flow so that the speed and character dilute than the first, and it is added slowly while the pulp is continuously agitated as before. After the second addition of coagulant the pulp liquor should be free from any latex or emulsion, and

the end point in' this step is actually determined by the water or liquor becoming clear.

Pulp fibers treated according to this process will have a coating of resinous or rubber or the like particles throughout their entire length. The density and thickness of the coating will depend upon the amount of solid material added in the form of emulsion or latex. However. there will always be uniformity regardless of the density or thickness.

In order that the versatility of the process may I be understood a few examples of pulp treated according to the hereinabove described process v will be set out hereinbelow:

Example No. 1

Concen- Dry Wet Material tration Weight Weight (Percent) (Grams) (Grams) '2, 000 5, 000 Aluminum Sulphate 1 150 Latex of Buna Synthetic Rubber,

Type III; 20 24' 120 Aluminum Sulphate 0. 125 400 The rubber latex was stabilized and diluted to about 2% to 3% solids. After the first addi tion of aluminum sulphate the pulp was agitated by air for ten minutes, as was done in each of the other examples herein described, and the complete process carried out as set forth The total synthetic rubber in the coated pulp was slightly more than 54 A;%.

In this, and subsequent examples, reference to I Buna synthetic rubber type III is meant G. R. S. synthetic rubber type III.

Example No. v2

Concen- Dry Wet Material tration Weight Weight (Percent) (Grams) (Grams) Pulp 1 20 2, 000 Water 5,000 Aluminum Sulphate 1 150 Latex of Buua Synthetic Rubber,

Type III 20 20 100 Curing Agent (dispersion) 50 2 4 Aluminum Sulphate 0. 125 200 The process was carried out in exactly the same fashion as Example No. 1 except that the dispersion of curing agent was added after the latex and before the second addition of aluminum sulphate. In this process curing agents such as antioxidants, activators, sulphur and accelerators in the form of dispersions may be added-but if so should be added before the second addition of coagulant. In Example No. 2 the solids are 52.4% of the total.

In this example, a pigment, carbon black (P-3 3), was added to the pulp in a dispersion immediately after the addition of the latex and curing agent but before the second addition of aluminum sulphate. Such pigments are added for a variety of reasons such as to impart color or to increase the tensile strength of the sheet material made from the pulp. If a pigment is to be incorporated it may be mixed with the emulsion or latex or added separately in a dispersion. If added separately it must be added before the second addition of coagulant. The percentage of added solids in Example No. 3 is approximately 51.8% of the total weight.

Example No. 4

The amount of added solids is 51.6% of the total weight. P-33 is carbon black. "Acrawax C. is the trade name for a wax sold by Glycol Products Co. of New York. It is added in dispersion in the same manner as a pigment and increases the water resistance of the finished product.

marc es persion of para-formaldehyde wasaddedafter, 'the'addition of the latex'and before the second addition of aluminum sulphate.

Example N o. 6

Concen- Dry "Wet Ivlaterial f tration Weight .Weigiht .(Pcrccnt) (Grams) (Grams) Pul l 20 2,000

Water -.5;'000

Aluminum Sulphate 1 150 Latex of vinyl chloride 20 20 100'-- Aluminum Sulphate 0.125 200 The latex of vinyl chloride is that sold by B. F. Goodrich Co. under its trade-mark Geon; it is type PX-8. The latex was diluted to 2% to 3% solids. This is an example of an added thermoplastic type resin, which constituted 50% not the weight of the finished product.

Example No. 7

Ooncen- Dry Wet \lateriul tration Weight Weight (Percent) (Grams) (Grams) ..2, 000 5, 000 .lp I50 a r; of Styrene, 1' 58 20 "100 Ali'iminum Sulphate x125 :i-400 Styrene 4 -580 is a vinyl type, thermoplastic resin manufactured by DowChemicalsCo. The latex was diluted to 2% to 3% solids.

Example No. 8

v The resinisof the phenol formaldehyde ther- .mosetting resin and its emulsionis sold byDurez Plastics & Chemicals, Inc. under the No. MRO. "It has a pH value of and wasdiluted toiz'lt'ato Thewamount 10f. added solids'is .*.-39.5% 201 athe totali-weight. The latex of Buna. rubberzrwas r-stabllized and blended with'the Cumar. resin 5 emulsion-rand then diluted -.to 2% -to-;3-%.-solids.

.Concen-. ...Dry Wet Material vtiation Weight Weight; "'51) (Percent) (Gi'ams) (Grams) Pulp 1 +20- S's-2,000 Water. 5,000 Aluminum Su 150 Dui'ezs Pheno n7o 200 Aluminum Sulphate...........-... ---600 'Cumar 25 resin .is a petroleum product.

Example No.10

' ,Concen- Dry Wet Material tration Weight Weight (Percent) (Grams) (Grams) 'Pulp .1 20 2,000

Water 5,000

Aluminum Sulphate 1 150 Latex of Neoprene Synthetic RubbenNo. 571 .20 8. 3 .41. 5

Ester type plasticizer emulsion-.. 20 2.8 14.0

"Curing agent (dispersion) 1.5 3

Aluminum Sulphate 0.125 .200

' The ester type plasticizer-issold'by'Monsanto "Chemical "Co. under the designation B'-l6.'1It

'"was "dilutedto 2% to 3% solids.

After the 'pulp has beenztreated according to "the present inventionto'coat'the individual fibers with a rubber, resinous or the like materiaL'the pulp may be :formed into sheets 'on a conventional machine operated pinr'the: conventional' manner.

Some of the finished products made from the improved sheeting "formed from pulpr' treated according to this invention-includegasketsysheet packing, high strength papers, waterandroil resistant papers, backing for pressure "sensitive adhesives, imitation leathers, electrical. insulating boards and panels, and the' like.

While preferred embodiment and examples-of "the invention have been idescribedpit swillsbe appreciated that numerous changes, variations and modifications may" beimade in the: process without departing, from the aspiritzand scope of .the invention. Whatis claimedas .new and de- -2sired to be secured by United .statestLetters Patentis:

,1. Inthe process of preparinga coated fibrous ..material, the improvement. which .consistsin providing an aqueous slurry containing not .more than about 2% of fiber, subjecting .the slurry continuously to rapid, turbulent mass. agitation by bubbling .upwardly therethrough a gas whereby the fibers are continuously disperscdbythe expanding gas bubbling'therethrough, and slowly adding to the ebullient slurry a coating material in the form of an emulsion whereby the dispersed fibers are uniformly coated with the coating material.

"2. The processes set forth in claim 1 in which a coagulant is added to the slurry prior to the introduction into the slurry. of the .coating-ma- -.terial to thereby precondition the fibers for the reception and retention of the coating material, and a more dilute coagulant is added to the "ebullient slurry after the coating of thefibers has commenced to thereby achieve substantially retention of the coating material by the fibers.

3. The processes set forthinclaim lin which the coating material is a rubber latex .and in which the latex emulsion contains about 2 to 10% of solids.

' 4. The process of coating fibers with emulsifiable material which comprises providing a dilute aqueous slurry of the fibers with the fiber content of .the slurry being not more than.2% by weight, subjecting the slurry continuously .to rapid, turbulent massagitationby bubbling upwardly therethrough a gas wherebythe'fibersare continuously dispersed by the expanding gas bubbling therethrough, and slowly adding to the ebullient slurry in the form of an emulsion a coating material selected from a group comprising natural and synthetic rubber, thermoplastic and thermosetting resins, waxes and oils, and in which the emulsion contains from about 2 to 10% solid material, said coating material being effectively dispersed throughout the slurry by said ebullient gas agitation whereby the dispersed fibers are uniformly coated with the coating material.

5. The process as set forth in claim 4 in which a polyvalent coagulant is added to the slurry with from about 50 to 90% of the coagulant being added prior to the introduction into the slurry of the coating emulsion and the remainder is added to the slurry in more dilute form during the coating step to obtain substantially complete retention of the coating material by the fibers.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 981,093 McCaskell Jan. 10, 1911 1,502,686 Schidrowitz July 29, 1924 1,607,519 Ellis Nov. 16, 1926 1,673,047 Hawley June 12, 1928 Number 10 Name Date Goebels Aug. 28, 1934 Campbell Jan. 12, 1937 Rosmait Feb. 8, 1938 Fisher Mar. 29, 1938 Goebels Aug. 9, 1938 Rosmait Nov. 1, 1938 Kress Jan. 9, 1940 Hines May 14, 1940 Lowe Oct. 29, 1940 Pare July 7, 1942 Scott Sept. 21, 1943 Pretzel May 8, 1945 Stevens Nov. 12, 1946 Osborne Jan. 28, 1947 lleubert et a1. Dec. 27, 1949 Wilson Aug. 14, 1951 Wilson et al June 24, 1952 OTHER. REFERENCES Collins et al., Paper Trade J., September 25, 1941, pp. 94-99.

Price, Paper Trade J November 20, 1947, pp.

25 Manufacture of Pulp and Paper 3rd Ed., vol. IV.

Sec. 5, pp. 2, 18 and 21 (1938).

Sutermeister, Tech. Assoc. Papers, Series EX, pp. 470 and 473, 1936. 

1. IN THE PROCESS OF PREPARING A COATED FIBROUS MATERIAL, THE IMPROVEMENT WHICH CONSISTS IN PROVIDING AN AQUEOUS SLURRY CONTAINING NOT MORE THAN ABOUT 2% OF FIBER, SUBJECTING THE SLURRY CONTINUOUSLY TO RAPID, TURBULENT MASS AGITATION BY BUBBLING UPWARDLY THERETHROUGH A GAS WHEREBY THE FIBERS ARE CONTINUOUSLY DISPERSED BY THE EXPANDING GAS BUBBLING THERETHROUGH, AND SLOWLY ADDING TO THE EBULLIENT SLURRY A COATING MATERIAL IN THE FORM OF AN EMULSION WHEREBY THE DISPERSED FIBERS ARE UNIFORMLY COATED WITH THE COATING MATERIAL. 